1. Field of the Invention
The present invention relates to an optical communication device and a method of fixing an optical module.
2. Description of the Related Art
In a conventional optical communication device, an optical module has an optical element and a lens system housed in a package. The optical module in turn has a mounting base which longitudinally protrudes at four positions in the lower portion of the package in the form of a flange. Screw holes are formed through the mounting base so that the optical module is secured by screwing the mounting base on a supporting member such as a circuit board and a heat sink.
For preventing the transmission loss of light transmitted through an optical fiber as much as possible to achieve a high coupling efficiency, a conventional optical module must be precisely assembled such that the optical axis of its optical element and lens system are in alignment with the optical axis of the optical fiber. However, since the optical module is designed to be screwed on a supporting member such as a circuit board and a heat sink through the mounting base, a stress associated with the screwing directly acts on the package. For this reason, the optical module has a problem in that the bottom plate of the package can be deformed, when it is mounted on the supporting member, causing a shift of the optical axis of the optical element and lens system from the optical axis of the optical fiber, resulting in a possible reduction in the coupling efficiency after it is mounted.
In an optical module which uses a laser diode as an optical element, on the other hand, since the laser diode generates a large amount of heat, a temperature control device such as a Peltier device is used to forcibly cool the optical module, and its package is made in a small thickness to enhance a heat dissipation effect. Thus, such an optical module may be easily deformed due to an externally applied force, heat and so on since the package is thin and accordingly relatively low in strength. Therefore, in the optical module which is so designed that the package is screwed on the heat sink, thermal expansion of the heat sink deforms the bottom plate of the package, causing the optical axis to easily shift as mentioned above.
Particularly, a laser diode having large power on the order of 100 mW or more, for use as an excitation light source for an optical fiber amplifier, is applied with an injection current close to its limit of performance in order to provide high output. Thus, with an optical module which uses such a laser diode, even the slightest shift of the optical axis results in significant reduction in the coupling efficiency, so that it is necessary to avoid reduced power caused by the optical system to the utmost. Moreover, an optical fiber amplifier which uses such an optical module has the problem that it cannot achieve expected output characteristics if the coupling efficiency is reduced.
It is an object of the present invention to provide an optical communication device and a method of fixing an optical module which are capable of avoiding an unwanted stress acting on the optical module during the mounting to prevent a reduction in the coupling efficiency caused by a shift of the optical axis of an optical element and a lens system from the optical axis of an optical fiber.
To achieve the above object, an optical communication device according to the present invention has an optical module which has an optical element and a lens system optically coupled together through a space and housed in a package, and a supporting member for supporting the optical module, wherein a fixing member is directly placed over the optical module for removably fixing the optical module to the supporting member, so that the optical module is securely sandwiched between the fixing member and the supporting member.
Also, to achieve the above object, in a method of fixing an optical module on a supporting member according to the present invention, wherein the optical module has an optical element and a lens system optically coupled through a space and housed in a package. The method comprises the step of removably fixing the optical module on the supporting member by a fixing member directly placed over the optical module such that the optical module is sandwiched between the supporting member and the fixing member.
As the optical module is placed between the supporting member and the fixing member and removably sandwiched securely between the fixing member and the supporting member, a stress associated with the fixation, when the optical module is mounted, acts on the optical module through the fixing member, and the optical module is additionally pressed by the fixing member onto and in planar contact with the supporting member, thereby preventing the optical axis from shifting. This optical module is used as an excitation light source, and optically connected to an excitation optical fiber doped with a rare earth element, thereby allowing the optical communication device (optical fiber amplifier) to achieve expected power characteristics.
According to a preferred embodiment of the present invention, it is possible to provide an optical communication device, and a method of fixing an optical module which avoid an unwanted stress acting on the optical module when the optical module is mounted, and can prevent a reduction in a coupling efficiency resulting from a shift of the optical axis of an optical element and a lens system from the optical axis of the optical fiber.
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.